To date, most in vitro approaches have utilized sarcoidal tissue suspensions (Kveim suspensions) to stimulate specifically morphologic and metabolic changes in leukocytes of patients with sarcoidosis. For the forseeable future, such sarcoidal tissue suspensions may prove to be an essential element in the devising of an in vitro test in sarcoidosis. Our laboratory has been making a systematic effort to purify, solubilize, isolate, and characterize by currently available physical and chemical techniques, the active components present in human sarcoidal tissues which are responsible for eliciting a positive intracutaneous Kveim reaction in responsive subjects with active sarcoidosis. Once this active fraction is identified, either a substitute test antigen, independent of human sarcoidal tissue, sources might be found or with the purified active principle in hand, a reliable in vitro Kveim test may be devised.